A DC-DC converter converts a direct current (DC) power source from one voltage level to another. A DC-DC converter may be, for example, a Buck DC-DC converter in which the input voltage is higher than the output voltage, a Boost DC-DC converter in which the input voltage is lower than the output voltage, or a Buck-Boost DC-DC converter in which the input voltage is higher or lower than the output voltage. Constant on-time voltage regulators, such as buck DC-DC converters, boost DC-DC converters, or buck-boost DC-DC converters, are known for their fast transient responses, ease of design, and smaller and simpler controllers.
However, a typical constant-on-time pulse generator uses analog circuits for pulse signal generation. However, analog circuits may not work well with a DC-DC converter that switches at a high frequency. For example, a constant-on-time pulse generator may use a ramp generator and a comparator with a fixed threshold to generate a pulse signal with a fixed pulse width. However, because of the comparator's finite propagation delay, the constant-on-time pulse generator does not work well when the DC-DC converter switches at a high frequency. Specifically, because of the comparator's finite propagation delay, the constant-on-time pulse generator may not able to generate a pulse signal with a pulse width that is narrow enough for the high switching frequency of the DC-DC converter.